Systems and methods for electrically detecting the presence of exudate in dressings

ABSTRACT

Systems and methods are provided for sensing fluid in a dressing on a patient and producing an electrical signal. In one instance, a galvanic cell is used as an electronic detection device. The galvanic cell is placed in the dressing and produces voltage when the dressing is substantially saturated. In one instance, the dressing is a reduced-pressure, absorbent dressing. Other systems, methods, and dressings are presented.

RELATED APPLICATION

The present invention claims the benefit, under 35 USC §119(e), of thefiling of U.S. Provisional Patent Application Ser. No. 61/365,614,entitled “Inflatable Off-loading Wound Dressing Assemblies, Systems, andMethods,” filed 19 Jul. 2010, which is incorporated herein by referencefor all purposes; U.S. Provisional Patent Application Ser. No.61/407,194, entitled “System and Methods For Electrically Detecting ThePresence of Exudate In Reduced-Pressure Dressings,” filed 27 Oct. 2010,which is incorporated herein by reference for all purposes; and U.S.Provisional Patent Application Ser. No. 61/418,730, entitled “Systemsand Methods for Electrically Detecting the Presence of Exudate inDressings,” filed 1 Dec. 2010, which is incorporated herein by referencefor all purposes.

FIELD

The present disclosure relates generally to medical treatment systemsand, more particularly, but not by way of limitation, to systems andmethods for electrically detecting the presence of exudates indressings, such as absorbent, reduced-pressure dressings.

BACKGROUND

Clinical studies and practice have shown that providing a reducedpressure in proximity to a tissue site augments and accelerates thegrowth of new tissue at the tissue site. The applications of thisphenomenon are numerous, but application of reduced pressure has beenparticularly successful in treating wounds. This treatment (frequentlyreferred to in the medical community as “negative pressure woundtherapy,” “reduced pressure therapy,” or “vacuum therapy”) provides anumber of benefits, which may include faster healing and increasedformulation of granulation tissue. Typically, reduced pressure isapplied to tissue through a porous pad or other manifold device. Theporous pad contains cells or pores that are capable of distributingreduced pressure to the tissue and channeling fluids that are drawn fromthe tissue. Reduced pressure may also be used to remove fluids and forother purposes.

SUMMARY

According to an illustrative embodiment, a dressing for receiving andretaining an ionic fluid includes an absorbent layer for placing influid communication with the tissue site and for receiving and retainingthe ionic fluids. The absorbent layer has a first side and a second,patient-facing side. The dressing further includes a sealing member forcovering the absorbent layer and a first galvanic cell associated withthe absorbent layer. The first galvanic cell is configured to produce avoltage when the absorbent layer proximate to the first galvanic cell issubstantially saturated with the ionic fluid.

According to another illustrative embodiment, a system for treating atissue site on a patient with reduced pressure includes an absorbentlayer for placing proximate to the tissue site, a sealing member forcovering the dressing and a portion of the patient's epidermis to form afluid seal, and a reduced-pressure source fluidly coupled to theabsorbent layer for providing reduced pressure to the absorbent layer.The system further includes a galvanic cell associated with theabsorbent layer. The galvanic cell is configured to produce a voltagewhen the absorbent layer proximate to the galvanic cell is substantiallysaturated with an ionic fluid. The system may also include a monitoringunit electrically coupled to the galvanic cell for receiving power orvoltage from the galvanic cell.

According to another illustrative embodiment, a method for treating atissue site includes providing a dressing. The dressing includes anabsorbent layer for placing in fluid communication with the tissue siteand for receiving and retaining ionic fluids. The absorbent layer has afirst side and a second, patient-facing side. The dressing also includesa sealing member for covering the absorbent layer and includes a firstgalvanic cell associated with the absorbent layer. The first galvaniccell is configured to produce a voltage indicative of a full state whenthe absorbent layer proximate to the first galvanic cell issubstantially saturated with the ionic fluid. The method also includesdeploying the dressing proximate to the tissue site and electricallycoupling the first galvanic cell to a monitoring unit. The monitoringunit is configured to produce a dressing-full signal when receiving avoltage indicative of a full state from the first galvanic cell. Themethod further includes providing reduced pressure to the dressing untilthe monitoring unit provides the dressing-full signal.

According to another illustrative embodiment, a dressing for treating atissue site on a patient includes an absorbent layer for placing influid communication with the tissue site and for receiving and retainingionic fluids. The absorbent layer has a first side and a second,patient-facing side. The dressing further includes a sealing member forcovering the absorbent layer and a conductive loop fluidly coupled tothe absorbent layer. The conductive loop has a first terminal, a secondterminal, and at least one conductive gap. The conductive gap is sizedand configured to be electrically bridged when covered with the ionicfluid.

According to another illustrative embodiment, a dressing for treating atissue site on a patient includes an absorbent layer for placing influid communication with the tissue site and for receiving and retainingfluids. The absorbent layer has a first side and a second,patient-facing side. The dressing further includes a dye associated withthe absorbent layer. The dye is operable to change colors when becomingwet. The dressing also includes a sealing member for covering theabsorbent layer and an electrical optical sensor associated with theabsorbent layer. The electrical optical sensor is configured to detect achange in color of the dye associated with the absorbent layer and toproduce a signal when the change has been sensed.

According to another illustrative embodiment, a reduced-pressuretreatment system includes a treatment manifold for placing in fluidcommunication with a tissue site and for receiving ionic fluids. Thetreatment manifold has a first side and a second, patient-facing side.The reduced-pressure treatment system further includes a sealing memberfor covering the treatment manifold, an absorbent layer disposed betweenthe sealing member and the treatment manifold, an electronic detectiondevice associated with the absorbent layer for producing an electricalsignal indicative of at least a fully saturated state, and awireless-communication-and-power subsystem. Thewireless-communication-and-power subsystem includes an antenna,communication, and processing unit associated with the electronicdetection device and a remote wireless communication and power unitconfigured to transmit power to the antenna, communication, andprocessing unit and to receive a signal therefrom.

Other features and advantages of the illustrative embodiments willbecome apparent with reference to the drawings and detailed descriptionthat follow.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a schematic diagram with a portion shown in cross section ofan illustrative embodiment of a reduced-pressure treatment systememploying a galvanic cell to electrically sense the presence ofexudates;

FIG. 2 is a schematic diagram of an illustrative embodiment of galvaniccell on a wound dressing;

FIG. 3 is a schematic cross section of a portion of an illustrativeembodiment of a dressing with a conductive loop;

FIG. 4A is a schematic top view of an illustrative embodiment of aconductive loop for use with a dressing, such as the dressing in FIG. 3,showing a plurality of conductive gaps;

FIG. 4B is a schematic side view of the conductive loop of FIG. 4A;

FIG. 5 is a schematic diagram of an illustrative embodiment of a circuitfor use with the conductive loop of FIGS. 4A-4B; and

FIG. 6 is a schematic diagram of an illustrative embodiment of areduced-pressure treatment system that includes awireless-communication-and-power subsystem.

DETAILED DESCRIPTION OF ILLUSTRATIVE EMBODIMENTS

In the following detailed description of the illustrative embodiments,reference is made to the accompanying drawings that form a part hereof.These embodiments are described in sufficient detail to enable thoseskilled in the art to practice the invention, and it is understood thatother embodiments may be utilized and that logical structural,mechanical, electrical, and chemical changes may be made withoutdeparting from the spirit or scope of the invention. To avoid detail notnecessary to enable those skilled in the art to practice the embodimentsdescribed herein, the description may omit certain information known tothose skilled in the art. The following detailed description is,therefore, not to be taken in a limiting sense, and the scope of theillustrative embodiments are defined only by the appended claims.

Referring now to the drawings and initially to FIG. 1, an illustrativeembodiment of a reduced-pressure treatment system 100 and a dressing 101for treating a tissue site 104, such as a wound 102, is presented. Thewound 102 may be centered in a wound bed. The wound 102 may be throughor involve epidermis 103, dermis 105, and subcutaneous tissue 107. Thereduced-pressure treatment system 100 may also be used at other tissuesites. The tissue site 104 may be the bodily tissue of any human,animal, or other organism, including bone tissue, adipose tissue, muscletissue, dermal tissue, vascular tissue, connective tissue, cartilage,tendons, ligaments, or any other tissue. Unless otherwise indicated, asused herein, “or” does not require mutual exclusivity.

The reduced-pressure treatment system 100 includes a treatment manifold108 and an absorbent layer 115. Absorbent in the context of theabsorbent layer or absorbent dressing means capable of at leasttemporarily retaining liquids. In addition, the reduced-pressuretreatment system 100 may include a sealing member 111 and areduced-pressure subsystem 113.

The treatment manifold 108 has a first side 110 and a second,patient-facing side 112. In one illustrative embodiment, the treatmentmanifold 108 is made from a porous and permeable foam or foam-likematerial and, more particularly, a reticulated, open-cell polyurethaneor polyether foam that allows good permeability of wound fluids whileunder a reduced pressure. One such foam material that has been used isthe VAC® GranuFoam® Dressing available from Kinetic Concepts, Inc. (KCI)of San Antonio, Tex. The manifold may be any substance or structure thatis provided to assist in applying reduced pressure to, delivering fluidsto, or removing fluids from the tissue site 104. A manifold typicallyincludes a plurality of flow channels or pathways. The plurality of flowchannels may be interconnected to improve distribution of fluidsprovided to and removed from the area of tissue around the manifold.Examples of treatment manifolds 108 may include, without limitation,devices that have structural elements arranged to form flow channels,cellular foam, such as open-cell foam, porous tissue collections, andliquids, gels, and foams that include or cure to include flow channels.

In one embodiment, the treatment manifold 108 may be constructed frombioresorbable materials that do not have to be removed from a patient'sbody following use of the dressing 101. Suitable bioresorbable materialsmay include, without limitation, a polymeric blend of polylactic acid(PLA) and polyglycolic acid (PGA). The polymeric blend may also includewithout limitation polycarbonates, polyfumarates, and capralactones. Thetreatment manifold 108 may further serve as a scaffold for newcell-growth, or a scaffold material may be used in conjunction with thetreatment manifold 108 to promote cell-growth. A scaffold is a substanceor structure used to enhance or promote the growth of cells or formationof tissue, such as a three-dimensional porous structure that provides atemplate for cell growth. Illustrative examples of scaffold materialsinclude calcium phosphate, collagen, PLA/PGA, coral hydroxy apatites,carbonates, or processed allograft materials.

The absorbent layer 115 has a first side 117 and a second,patient-facing side 119. The absorbent layer 115 may be used alone orwith the treatment manifold 108 or omitted from the reduced-pressuretreatment system 100. The absorbent layer 115 may be coupled to thefirst side of the treatment manifold 108 or merely disposed proximate tothe first side of the treatment manifold 108. The absorbent layer 115may be formed with one or more layers including a wicking layer and astorage layer. For example, the absorbent layer 115 may be formed fromsuperabsorbent polymers (SAP) of the type often referred to as“hydrogels,” “super-absorbents,” or “hydrocolloids.” The absorbent layer115 may also be formed from alginates or cellulose based materials.

The sealing member 111 covers the treatment manifold 108 and absorbentlayer 115 and extends past a peripheral edge 114 of the treatmentmanifold 108 and absorbent layer 115 to form a sealing-member extension116. The sealing-member extension 116 has a first side 118 and a second,patient-facing side 120. The sealing-member extension 116 may be sealedagainst the epidermis 103 or against a gasket or drape by a sealingapparatus 124, such as a pressure-sensitive adhesive 126. The sealingapparatus 124 may take numerous forms, such as an adhesive sealing tape,or drape tape or strip; double-sided drape tape; pressure-sensitiveadhesive 126; paste; hydrocolloid; hydrogel; or other sealing means. Ifa drape tape is used, the tape may be formed of the same material as thesealing member 111 with a pre-applied, pressure-sensitive adhesive 126.The pressure-sensitive adhesive 126 may be applied on the second,patient-facing side 120 of the sealing-member extension 116. Thepressure-sensitive adhesive 126 provides a substantial fluid sealbetween the sealing member 111 and the epidermis 103, which, as usedherein, may also deemed to include a gasket or drape against theepidermis 103. Before the sealing member 111 is secured to the epidermis103, removable strips (not shown) covering the pressure-sensitiveadhesive 126 may be removed. A fluid seal is adequate to maintainreduced pressure at a desired site given the particular reduced-pressuresource or subsystem involved.

The sealing member 111 may be an elastomeric material or any material orsubstance that provides a fluid seal. Elastomeric means having theproperties of an elastomer and generally refers to a polymeric materialthat has rubber-like properties. More specifically, most elastomers havean ultimate elongations greater than 100% and a significant amount ofresilience. The resilience of a material refers to the material'sability to recover from an elastic deformation. Examples of elastomersmay include, but are not limited to, natural rubbers, polyisoprene,styrene butadiene rubber, chloroprene rubber, polybutadiene, nitrilerubber, butyl rubber, ethylene propylene rubber, ethylene propylenediene monomer, chlorosulfonated polyethylene, polysulfide rubber,polyurethane (PU), EVA film, co-polyester, and silicones. Further still,the sealing member 111 may include a silicone drape, 3M Tegaderm® drape,PU drape such as one available from Avery Dennison Corporation ofPasadena, Calif.

The reduced-pressure subsystem 113 includes any device or devices thatsupply reduced pressure to the tissue site 104, and typically, to thetreatment manifold 108. The reduced-pressure subsystem 113 typicallyincludes a reduced-pressure source 140, which may take many differentforms. The reduced-pressure source 140 provides reduced pressure as apart of the reduced-pressure treatment system 100. Reduced pressuregenerally refers to a pressure less than the ambient pressure at atissue site 104 that is being subjected to treatment. In most cases,this reduced pressure will be less than the atmospheric pressure atwhich the patient is located. Alternatively, the reduced pressure may beless than a hydrostatic pressure at a tissue site. Unless otherwiseindicated, values of pressure stated herein are gauge pressures.

The reduced pressure delivered may be constant or varied (patterned orrandom) and may be delivered continuously or intermittently. Consistentwith the use herein, an increase in reduced pressure or vacuum pressuretypically refers to a relative reduction in absolute pressure.

A portion 146 of the reduced-pressure delivery conduit 144 may have oneor more devices, such as a representative device 148. The device 148 maybe, for example, a fluid reservoir to hold exudates and other fluidsremoved, a pressure-feedback device, a volume detection system, a blooddetection system, an infection detection system, a flow monitoringsystem, or a temperature monitoring system. Multiple devices 148 may beincluded. Some of these devices 148 may be integrated with thereduced-pressure source 140.

The reduced-pressure source 140 may be any device for supplying areduced pressure, such as a portable therapy unit, a stationary therapyunit, micropump, or other device. While the amount and nature of reducedpressure applied to a tissue site will typically vary according to theapplication, the reduced pressure will typically be between −5 mm Hg(−667 Pa) and −500 mm Hg (−66.7 kPa) and more typically between −75 mmHg (−9.9 kPa) and −300 mm Hg (−39.9 kPa).

The reduced pressure developed by reduced-pressure source 140 isdelivered through the reduced-pressure delivery conduit 144 to areduced-pressure interface 150, which may include an elbow port 152. Inone illustrative embodiment, the reduced-pressure interface 150 is aT.R.A.C.® Pad or Sensa T.R.A.C.® Pad available from KCI of San Antonio,Tex. The reduced-pressure interface 150 allows the reduced pressure tobe delivered through the sealing member 111 to the treatment manifold108, as well as to a sealed treatment space 154, in which the treatmentmanifold 108 is located. In this illustrative embodiment, thereduced-pressure interface 150 extends through the sealing member 111and into the treatment manifold 108. In another illustrative embodiment,the reduced-pressure interface 150 delivers reduced pressure to theabsorbent layer 115 and the absorbent layer 115 delivers the reducedpressure to the treatment manifold 108.

While a reduced-pressure interface 150 is shown in FIG. 1, it should beunderstood that the reduced-pressure treatment system 100 may be usedwithout the reduced pressure interface 150. For example, thereduced-pressure delivery conduit 144 may be disposed through anaperture in the sealing member 111 and into the absorbent layer 115.Alternatively, the reduced-pressure delivery conduit 144 may be placedunder an edge of the sealing member 111 and into the absorbent 115 orthe treatment manifold 108 and sealed. The reduced-pressure deliveryconduit 144 may be sealed using, for example, a drape tape.

An electronic detection device 159 is used to determine when theabsorbent layer 115 is at least substantially saturated. The absorbentlayer 115 becomes substantially saturated when the absorbent layer 115fills with a liquid or when the area near the electronic detectiondevice 159 becomes wet from the position of the dressing. As an exampleof the electronic detection device 159, one or more galvanic cells,e.g., a first galvanic cell 160, may be associated with the absorbentlayer 115 to assess the presence of an ionic fluid, e.g., exudate. Theelectronic detection device 159 is typically placed such that theelectronic device 159 contacts the absorbent layer 115 at locationswhere liquid will gather as the absorbent layer 115 becomes saturated.The electronic detection device 159 may be located on the sealing member111 or within the absorbent material of the absorbent layer 115. Wherethe electronic detection devices 159 are mounted on the sealing member111, electrical contact can be made to the sensing hardware directlythrough apertures in the sealing member 111. When wires or the directcontact method is used, the wires or components extend through thesealing member 111. The wires or components are sealed with respect tothe sealing member 111 where the wires or components pass through thesealing member 111 in order to maintain the integrity of the reducedpressure, i.e., to maintain a fluid seal.

The first galvanic cell 160 produces a small current when the absorbentlayer 115 proximate to the first galvanic cell 160 is substantiallysaturated with the ionic fluid. Typically, the first galvanic cell 160will be located at a location that will experience the ionic fluid lastas the absorbent layer 115 receives fluids from the tissue site 104 orthe treatment manifold 108, and thereby functions as a full indicatorfor the absorbent layer 115. In other words, when the absorbent layer115 is saturated, the first galvanic cell 16 produces a signalindicative of the same.

The first galvanic cell 160 includes a first electrode 162 that iselectrically coupled to a first electrical lead 164. The first galvaniccell 160 also includes a second electrode 166 that is spaced from thefirst electrode 162 and that is electrically coupled to a secondelectrical lead 168. The first electrode 162 and second electrode 166are formed from different conducting materials suitable for use with agalvanic cell. For example, in one illustrative embodiment, the firstelectrode 162 is copper (Cu) and the second electrode 166 is tin (Sn).In another illustrative embodiment, the first electrode 162 is copper(Cu) and the second electrode 166 is zinc (Zn). In another illustrativeembodiment, the first electrode 162 is nickel (Ni) and the secondelectrode 166 is aluminum (Al). Almost any combination of materials onan electrochemical potential chart may be used, e.g., any combination oftwo of the following: F, Cl, Pt, Hg, Ag, I, Cu, Pb, Ni, Fe, Zn, Al, Na,Ca, K, or Li. The selected combination of metals should be dissimilar.Alloys will impact the exact voltage measured. Some combinations ofmetals on the list of metals would not be practical if elementally pure,such as Li, K and others.

A monitoring unit 170 is electrically coupled to the first electricallead 164 and the second electrical lead 168 and is configured to detectvoltage, current, or power generated by the first galvanic cell 160. Asshown in FIG. 2, the voltage across 272 could be presented to adifferential amplifier, or used in a single ended fashion with one endof 272 grounded and the other end presented to an operational voltageamplifier (OP AMP). The monitoring unit 170 includes a circuit formeasuring the power or voltage produced, e.g., a comparator circuit.When the ionic fluid substantially saturates the absorbent layer 115proximate to the first and second electrodes 162, 166, the ionic fluidfunctions as a salt bridge between the two electrodes 162, 166 andcurrent is produced. The monitoring unit 170 may include a visual or anaudible alarm that signals when a threshold power or current has beenreached. The alarm, or dressing full signal, signifies that the dressing101 is full, and more specifically, that the absorbent layer 115 isfull.

In operation, according to one illustrative embodiment, the treatmentmanifold 108 is deployed proximate to the tissue site 104, e.g., in thewound bed on the wound 102, with a portion near a wound edge 109. Theabsorbent layer 115 is placed proximate to the treatment manifold 108(if not already attached) to receive ionic fluids. The first galvaniccell 160 is applied to the absorbent layer 115. The sealing member 111is placed over the tissue site 104 and the treatment manifold 108 and atleast partially against epidermis 103 (or gasket or drape) to form afluid seal and to form the sealed treatment space 154. If not alreadyinstalled, the reduced-pressure interface 150 is installed. Thereduced-pressure delivery conduit 144 is fluidly coupled to thereduced-pressure interface 150 and the reduced-pressure source 140whereby reduced pressure may be provided to the treatment manifold 108.The reduced-pressure source 140 may be activated to begin the deliveryof reduced pressure to the treatment manifold 108 in the sealedtreatment space 154.

The reduced pressure delivered will extract exudates into the treatmentmanifold 108. The exudates are absorbed, at least in part, from thetreatment manifold 108 by the absorbent layer 115 and eventually willsubstantially saturate the absorbent layer 115. As previously discussed,the saturated absorbent layer 115 functions as a salt bridge and thefirst galvanic cell 160 provides a current flow that may be detected andused to sound an alarm or produce a signal indicating that the absorbentlayer 115 is full.

While the illustrative embodiment of FIG. 1 is shown with reducedpressure applied and with a treatment manifold 108, it should beunderstood that in other embodiments, the absorbent layer 115 may beplaced directly proximate to a tissue site. In addition, areduced-pressure source may not be used to attract exudates or otherionic fluids, but rather a wicking layer may be used with the absorbentlayer 115 to attract fluids. It should also be appreciated that aplurality of galvanic cells may be used to provide progressive feedbackon the state of fill of the absorbent layer 115. The plurality ofgalvanic cells may be located in geometrically significant areas whereliquids are expected to collect. The positions could also be chosen toindicate the progress of the liquid through the dressing 101 so that anestimation of remaining capacity may be calculated.

Referring now primarily to FIG. 2, a system 200 for treating a tissuesite on a patient is shown. The system 200 includes a dressing 201 andan electronic detection device 159. The electronic detection device 159may include a first galvanic cell 260. The first galvanic cell 260includes a first electrode 262 electrically coupled to a firstelectrical lead 264. The first galvanic cell 260 includes a secondelectrode 266 electrically coupled to a second electrical lead 268. Thefirst and second electrodes 262, 266 may be coupled to a base 263, orstabilizing platform. A power-using device, e.g., a resistor 272, may beelectrically coupled between the first electrical lead 264 and thesecond electrical lead 268. A voltage may be measured between theelectrical leads 264, 268 by a monitoring unit 270. The voltage betweenthe electrodes 262, 266 will rise above a threshold value as theabsorbent layer 115 becomes saturated proximate to the electrodes 262,266. In one illustrative, non-limiting embodiment, the longitudinallength of the base 263 is 20 mm, the width is 10 mm, and the electrodesare 8 mm by 8 mm.

The monitoring unit 270 may produce an analog signal indicative of thevoltage and that signal may be delivered by a third lead 274 to ananalog-to-digital converter 276. A digital signal may then be deliveredby a fourth lead 278 to a microprocessor unit 280. The microprocessorunit 280 may monitor and manipulate the signal as desired. Upondetermining that a threshold value has been reached, the microprocessorunit 280 may provide a signal to an alarm 282 (visual or audible) or toanother unit.

Referring now primarily to FIGS. 3-5, another illustrative embodiment ofa reduced-pressure system 300 and dressing 301 is presented. Thereduced-pressure system 300 includes an electronic detection device 359.The electronic detection device 359 may include one or more conductiveloops, e.g., a first conductive loop 384, a second conductive loop 386,and a third conductive loop 388. It should be understood that the“conductive loops” are selectively conductive or only conductive attimes when the circuit is completed as is described herein. Similar tothe previously presented embodiments, the dressing 301 may include atreatment manifold 308 having a first side 310 and a second side 312.The dressing 301 includes an absorbent layer 315, which has a first side317 and a second, patient-facing side 319. In another illustrativeembodiment, the system 300 excludes the treatment manifold 308, and thesecond, patient-facing side 319 of the absorbent layer 315 is placedadjacent to the tissue site 304.

In the illustrative embodiment shown, the treatment manifold 308 isplaced proximate to the tissue site 304. The tissue site is a wound 302that extends through epidermis 303, through dermis 305 and intosubcutaneous tissue 307. A sealing member 311 is placed over theabsorbent layer 315 and optionally (if included) over the treatmentmanifold 308 to form a sealed space 354. Thus, the conductive loops 384,386, 388 are disposed under the sealing member 311 and proximate to theabsorbent layer 315. The conductive loops 384, 386, 388 are in thesealed space 354.

A reduced-pressure source 340 is covered by the sealing member 311 andprovides reduced pressure in the sealed space 354. The sealing member311 includes an aperture 323 to allow the reduced-pressure source 340 tovent. The reduced-pressure source 340 may be a micro pump, a diaphragmpump, disc pump, piezoelectric pump, or other small pump. In theillustrative embodiment, the reduced-pressure source is built into thedressing 301. A layer 343 may be included to help distribute reducedpressure or prevent fluids from entering the reduced-pressure source340. It should be understood that other sources of reduced pressure maybe utilized and in other embodiments may be excluded altogether. Thereduced-pressure source 340 may utilize a connecting member 341 tofluidly couple the reduced-pressure source 340 to the absorbent layer315. In another embodiment, the connecting member 341 may extend throughthe absorbent layer 315 and directly couple the reduced-pressure source340 to the treatment manifold 308.

According to an illustrative embodiment, in operation, as before, thedressing 301 receives exudates or other ionic fluid from the tissue site304 and stores the exudate in the absorbent layer 315. The absorbentlayer 315 may have a wicking layer to help pull exudate from thetreatment manifold 308. When the absorbent layer 315 becomes fullysaturated, the absorbent layer 315 will no longer hold additionalexudate. Accordingly, the patient or healthcare provider will want to bealerted when the absorbent layer 315 is saturated. The conductive loops384, 386, 388 (with speaker or visual alert or the another alert device)provide such an alert.

The plurality of conductive loops 384, 386, and 388 are added to theabsorbent layer 315 to help provide an indication of the fullness of theabsorbent layer 315. The first conductive loop 384 includes a firstterminal 385 and a second terminal 387. The first terminal 385 iscoupled by a first electrical lead 389 to a monitoring unit 370 thatincludes a first LED 371, a second LED 373, and a third LED 375. Thesecond terminal 387 is coupled by a second electrical lead 397 to themonitoring unit 370.

The monitoring unit 370 includes circuitry that provides power to theconductive loops 384, 386, and 388. The conductive loops 384, 386, 388contain conductive gaps 399 that are electrically bridged whensufficient exudate reaches the conductive loops 384, 386, 388.Sufficient exudate reaches the conductive loops at least when liquidsaturates the absorbent layer 315 in the area of the conductive loopinvolved as will be explained further below. The second conductive loop386 has a first terminal 390 and a second terminal 391. The firstterminal 390 and the second terminal 391 of the second conductive loop386 are electrically coupled by leads 393 and 394 to the monitoring unit370 and are particularly associated with second LED 373. Similarly, thethird conductive loop 388 includes leads 395 and 396 that areelectrically coupled to the monitoring unit 370 and are associated withthird LED 375.

FIGS. 4A and 4B show the first conductive loop 384, which isrepresentative of the other conductive loops 386, 388. The firstconductive loop 384 contains a conductive path 398 formed with one ormore conductive gaps 399. The conductive path 398 may be mounted on abase 379. To help safeguard against premature signaling, an electricalinsulation layer (not explicitly shown) may cover the conductive path398 and have apertures only at the conductive gaps 399. It will beappreciated that as an ionic fluid surrounds and covers the conductivepath 398, the ionic fluid will electrically couple the conductive gaps399. In other words, the ionic fluid serves as an electrical bridge forthe conductive gap 399 and allows the conductive path 398 to carry acurrent. When the current is carried sufficiently, the monitoring unit370 provides a signal, such as first LED 371. The other conductive loops386, 388 are analogous. It should be understood that while threeconductive loops 384, 386, and 388 are shown, any number of conductiveloops may be used. Multiple conductive loops may be used to assesssaturation of the dressing 301 at different locations and provide anescalating scale of fullness for the dressing 301.

Referring now primarily to FIG. 5, an illustrative embodiment of adetection circuit 400 is presented. Numerous circuit designs may be usedand detection circuit 400 is only an illustrative embodiment of one. Thedetection circuit 400 may be included in the monitoring unit 370. Thedetection unit 400 may be configured to power an LED 402 in response toa current flowing through the first terminal 385 and the second terminal387 indicating exudate in the dressing 301 as sensed by a completedconduction or conductive path. The detection circuit 400 may, forexample, provide a conductive loop that supplies a voltage from abattery 401 to the LED 402 in response to activation by a small currentpassing between the first terminal 385 and the second terminal 387.

The detection circuit 400 may utilize at least two capacitors 404 and406 to respond to the current through the first terminal 385 and thesecond terminal 387. A number of resistors 408, 410, 412, 414, 416, 418,and 420 in the detection circuit 400 generate voltage differentials thatfunction with the capacitors 404 and 406 to drive a NPN transistor 422and a PNP transistor 424 to activate the LED 402.

A completed conductive path across the first terminal 385 and secondterminal 387 allows current through the resistor 408 to bypass thecapacitor 404. Current flows through the resistor 410 to the base of theNPN transistor 422, rather than through the higher resistance pathprovided by resistor 412. The current entering the base of the NPNtransistor 422 amplifies the current allowed to flow into the NPNtransistor 422 through the resistors 414 and 416. The NPN transistor 422is “on” when the base is pulled high by the input signal through theresistor 410 relative to the emitter output.

The PNP transistor 424 is “on” when the base receiving current throughthe resistor 414 is pulled low relative to the emitter. As a result, thecurrent through the base of the NPN transistor 422 activates the PNPtransistor 424 to amplify current to the collector supplying current tothe resistor 418 and the LED 402. As a result, the NPN transistor 422and the PNP transistor 424 are only activated to supply a currentlighting the LED 402 in response to the first terminal 385 and thesecond terminal 387 completing a closed circuit or conductive path.

The detection circuit 400 may also include an output 426 that functionsas a terminal. The output 426 may communicate a signal received throughthe resistor 420 indicating that the PNP transistor 424 has beenactivated thereby supplying current through the LED 402. The output 426may communicate with a recording or logging device that records thepoint at which the conduction path was created between the firstterminal 385 and the second terminal 387. This information or data maybe utilized to track the presence of a threshold level of exudate in thedressing 301.

When the exudate within the dressing is insufficient to complete theconduction path between terminals 385 and 387, the detection circuit 400is inactive. The DC current passing through the resistor 408 from thebattery 401 is blocked by the capacitor 404. As a result, neither theNPN transistor 422 nor the PNP transistor 424 is activated to supplycurrent to the LED 402.

In other embodiments, the detection circuit 400 may be replaced by othercurrent detection circuits. The resistance, capacitance, and othercharacteristics of the detection circuit 400 may vary based on thesensitivity of the readings across the first terminal 385 and the secondterminal 387 and the power requirements of the LED 402. In anotherillustrative embodiment, the LED 402 may be replaced by a visual ordigital indicator that, based on the level of current passing throughthe resistor 418 to the indicator, indicates the amount or type ofexudate within the dressing 301. The indicator may be an analog ordigital element specifically calibrated to provide audible, visual, ortactile feedback to one or more users.

According to another illustrative embodiment, a capacitive senor may belocated on an exterior of the dressing, e.g., on the sealing member 111above where electrode 162 is shown in FIG. 1. The capacitive sensor hasa sensing profile that measures capacitance at a location that fillslast. When liquids reach the location that corresponds with the sensingprofile, the capacitance of the portion of the dressing associated withthe capacitive sensor changes within the dressing as seen by the fillsensor. As a result, the capacitance sensor produces a signal indicatingthat the dressing is saturated.

According to another illustrative embodiment, a dye is placed in theabsorbent layer, e.g., absorbent layer 315, that provides a changevisual appearance (or optical properties) upon becoming wet. The visualindication may be a change in contrast, change in color, change inbrightness, a change in reflectivity or other visual cue. The change invisual appearance may be a change perceptible to a human eye or only toa device, e.g., an electrical photo detector. The electrical photodetector may detect more subtle changes in visual appearance. Theelectrical photo detector is attached proximate to the sealing member311 and can optically detect the change in contrast and produce a signalindicative of the change. Thus, as the absorbent layer 315 becomessaturated, the dye changes contrast, the optical detector senses thechange in contrast, and develops a full signal. In another embodiment,the dye may be placed in the treatment manifold, e.g., manifold 108.

According to still another illustrative embodiment, metal capacitanceplates are put within or near the absorbent layer, e.g., absorbent layer315, having defined space between plates. The capacitance changes as theionic fluid fills the space between the plates. The change incapacitance is measured and the change is noted when the ionic fluidfills the space between the plates.

Referring now primarily to FIG. 6, a schematic diagram of anotherillustrative embodiment of a reduced-pressure treatment system 500 ispresented. The reduced-pressure treatment system 500 includes a wounddressing 501 that may include a manifold 508 and an absorbent layer 515.An electronic detection device 559 is associated with the absorbentlayer 515 and is configured to electronically determine when theabsorbent layer (or some portion thereof) is substantially saturated.The electronic detection device 559 may be, for example, a galvanic cellor a conductive loop with conductive gaps or other means ofelectronically determining when the absorbent layer 515 is substantiallysaturated.

Associated with the electronic detection device 559 is awireless-communication-and-power subsystem 571. Thewireless-communication-and-power subsystem 571 may provide power to theelectronic detection device 559 and may wirelessly receive informationrelated to the status of the absorbent layer 515 as produced by theelectronic detection device 559. The wireless-communication-and-powersubsystem 571 may include awireless-communication-and-power-transmission unit 572, which is on abase station 573, and an antenna-communication-and-processing unit 574.The wireless-communication-and-power subsystem 571 is analogous to aRadio-Frequency Identification Device (RFID). Power is transmitted by awireless signal 575 from thewireless-communication-and-power-transmission unit 572 to theantenna-communication-and-processing unit 574 from where the power isprovided by coupling 576 to the electronic detection device 559.

The power provided to the electronic detection device 559 may augmentpower already developed, e.g., by a galvanic cell, or provide all thepower, e.g., for a resistive circuit. In any event, the electronicdetection device 559 is configured to determine if the absorbent layer515 is saturated or possibly to what extent liquid exists within theabsorbent layer 515 and to produce a signal with the relevantinformation. The signal may be delivered by coupling 576 to theantenna-communication-and-processing unit 574 from where a wirelesssignal 575 carries the information to thewireless-communication-and-power-transmission unit 572. Thewireless-communication-and-power-transmission unit 572 may furtherprocess the signal for display or use by other systems monitoring orcontrolling the reduced-pressure treatment system 500. As such, withthis embodiment, no direct electronic connection is required between amonitoring device and the electronic detection device 559. Accordingly,less power may be needed and comfort may be enhanced.

The systems 100, 200, 300, 500 presented, allow for the saturation ofthe absorbent layer, e.g., 115, 215, 315, 515 to be determined using anelectrical device. Because a visual determination or a tactileinspection is not required, the electrical signal may be used to set offan alarm or otherwise signal the user or healthcare provider that thedressing is saturated and should be changed. Moreover, by arranging thecomponents, intermediate indications of the percentage full may beprovided. It should be understood that the output signal also enableseasy interface with an electronic controller or circuit in an analog ordigital system.

In another illustrative embodiment, the systems and methods forreceiving an ionic fluid may be analogous to the systems and methodspreviously presented, but the system may not utilize an absorbent layer,e.g., absorbent layer 115 in the reduced-pressure treatment system 100may be omitted. In such an embodiment, the electrodes are fluidlycoupled to a portion of a dressing that will be exposed to liquids lastas the liquids build up in the dressing. In still another embodiment,the dressings of FIGS. 1-4B, may be used without reduced pressure, butmay use wicking from the absorbent layer and may include additionalwicking layers. In this embodiment, a completed circuit would indicatesaturation of the dressing and signal a needed change.

Although the present invention and its advantages have been disclosed inthe context of certain illustrative embodiments, it should be understoodthat various changes, substitutions, permutations, and alterations canbe made without departing from the scope of the invention as defined bythe appended claims.

It will be understood that the benefits and advantages described abovemay relate to one embodiment or may relate to several embodiments. Itwill further be understood that reference to “an” item refers to one ormore of those items.

The steps of the methods described herein may be carried out in anysuitable order, or simultaneously where appropriate.

Where appropriate, aspects of any of the embodiments described above maybe combined with aspects of any of the other embodiments described toform further examples having comparable or different properties andaddressing the same or different problems. For example, each of thesensor types (galvanic sensors, conductive sensors, capacitive sensors)may be utilized with each of the pump types (external to the dressing,internal to the dressing, or without any pump). The various sensor typesmay be used in any number of combination of types as required.

It will be understood that the above description of preferredembodiments is given by way of example only and that variousmodifications may be made by those skilled in the art. The abovespecification, examples and data provide a complete description of thestructure and use of exemplary embodiments of the invention. Althoughvarious embodiments of the invention have been described above with acertain degree of particularity, or with reference to one or moreindividual embodiments, those skilled in the art could make numerousalterations to the disclosed embodiments without departing from thescope of the claims.

We claim:
 1. A system for treating a tissue site on a patient withreduced pressure, the system comprising: an absorbent layer adapted tobe disposed at the tissue site to receive fluids from the tissue site inresponse to reduced pressure; a sealing member for covering theabsorbent layer and a portion of an epidermis of the patient to form aseal; a reduced-pressure source adapted to be fluidly coupled to theabsorbent layer for providing reduced pressure to the absorbent layer; agalvanic cell comprising a cathode and an anode attached to a base andspaced apart from each other on the base, the cathode and the anodeadapted to contact the absorbent layer to form the galvanic cell; a loadelectrically coupled across the cathode and the anode to provide asignal when the absorbent layer contacts the cathode and the anode andbecomes substantially saturated with fluids from the tissue site; and amonitoring unit electrically coupled to the load and adapted to receivethe signal to provide an indication that the absorbent layer issaturated.
 2. The system of claim 1, wherein the monitoring unit is acomparator circuit.
 3. The system of claim 1, wherein the monitoringunit comprises an analog-to-digital converter coupled to amicroprocessor, and wherein the microprocessor is configured to developan alarm signal when the signal from the load reaches a signal thresholdvalue.
 4. The system of claim 1, wherein the cathode comprises copperand the anode comprises tin.
 5. The system of claim 1, wherein thecathode comprises copper and the anode comprises tin, and wherein thefluids comprise exudate.
 6. The system of claim 1, wherein the cathodecomprises copper and the anode comprises zinc.
 7. The system of claim 1,further comprising a plurality of galvanic cells associated with theabsorbent layer and configured to provide power proportional to thesaturation of the absorbent layer.
 8. The system of claim 1, wherein themonitoring unit comprises an electronic detection device and awireless-communication-and-power subsystem.
 9. The system of claim 1,wherein the load comprises a resistive load.
 10. The system of claim 1,wherein the load comprises a capacitive load.
 11. The system of claim 1,wherein a length of the base is 20 millimeters and a width of the baseis 10 millimeters.
 12. The system of claim 11, wherein a length of thecathode is 8 millimeters and a width of the cathode is 8 millimeters.13. The system of claim 11, wherein a length of the anode is 8millimeters and a width of the anode is 8 millimeters.
 14. The system ofclaim 11, wherein: a length of the cathode is 8 millimeters; a width ofthe cathode is 8 millimeters; a length of the anode is 8 millimeters;and a width of the anode is 8 millimeters.
 15. The system of claim 1,further comprising: a manifold adapted to be disposed between theabsorbent layer and the tissue site; wherein the cathode and the anodeare adapted to contact the absorbent layer opposite the manifold; andwherein the reduced-pressure source is adapted to be fluidly coupled tothe manifold.